The current invention relates to a high-frequency signal transmitter and in particular, to a high-frequency signal transmitter with a strip line-to-coplanar transition.
A known method for transmitting high-frequency signals, e.g. in microwave engineering, is to use aperture-coupled patch antennae. These are employed in antenna arrays, i.e. antenna arrangements with several of these patch antennae, or as individual emitters and/or couplers.
FIG. 4 shows a conventional aperture- or slot-coupled patch antenna. In FIG. 4, an antenna patch 19 is excited via a coupling slot 17 in a solid surface 18, the coupling slot 17 in turn being supplied by means of a supply line 16 with a free end 16 embedded in a buried plane. Underneath this plane 16 is another solid surface 12, that is connect in an electrically conductive fashion via interfacial connections 20 to the solid surface 18 provided with the coupling opening 17. A design of this kind is distinguished by a high transmission bandwidth. Between the supply line 16 and the coupling slot, there is usually a substrate b provided, in which the high-frequency energy of the signal to be transmitted or coupled into is linked to the slot or to the coupling opening 17. In microwave antenna arrangements or connections of this kind, the supply line 16 embedded in the substrate is usually provided in the form of a strip line. The HF energy of the signal is conveyed between the strip line 16 in the substrate and a solid surface 12, 18 on the top and bottom of the substrate.
But radiating the HF energy outward, e.g. into the air, from a substrate, is problematic, particularly when doing so from a substrate that has a high dielectric constant. For example, if low temperature cofired ceramic (LTCC)—which is suitable as a base material for microwave circuits—is used as the substrate material, then it becomes necessary to address the problem mentioned above since LTCC has a quite high dielectric constant of ∈r>4. This results in a reduction in antenna gain as well as a deterioration in antenna efficiency.